Christopher M. Deaton

Exercise-associated oxidative stress

Abstract During exercise a number of potential sources exist for the production of reactive oxygen species such as superoxide anions, hydrogen peroxide and hydroxyl radicals. Oxidative stress has been defined as a disturbance in the pro-oxidant-antioxidant balance in favour of the former, leading to potential damage (Sies 1991). Oxidative stress does not always result in oxidative damage. However, oxidative stress may result in oxidative damage to lipids, protein and DNA and consequently decrease athletic performance. Here we review the evidence for oxidative stress following exercise and the effects of exercise on the enzymatic and non-enzymatic antioxidant systems in a number of species including the horse. The effects of antioxidant supplementation on oxidative stress and performance during exercise are also evaluated.

Breath Condensate Hydrogen Peroxide Correlates with Both Airway Cytology and Epithelial Lining Fluid Ascorbic Acid Concentration in the Horse

The relationship between hydrogen peroxide (H2O2) concentration in expired breath condensate (EBC) and cytology of the respiratory tract obtained from tracheal wash (TW) or bronchoalveolar lavage (BAL), and epithelial lining fluid (ELF) antioxidant status is unknown. To examine this we analysed the concentration of H2O2 in breath condensate from healthy horses and horses affected by recurrent airway obstruction (RAO), a condition considered to be an animal model of human asthma. The degree of airway inflammation was determined by assessing TW inflammation as mucus, cell density and neutrophil scores, and by BAL cytology. ELF antioxidant status was determined by measurement of ascorbic acid, dehydroascorbate, reduced and oxidised glutathione, uric acid and α-tocopherol concentrations. RAO-affected horses with marked airway inflammation had significantly higher concentrations of breath condensate H2O2 than control horses and RAO-affected horses in the absence of inflammation (2.0±0.5 μmol/l, 0.4±0.2 μmol/l and 0.9±0.2 μmol/l H2O2, respectively; p<0.0001). The concentration of breath condensate H2O2 was related inversely to the concentration of ascorbic acid in ELF (r=-0.80; p<0.0001) and correlated positively with TW inflammation score (r=0.76, p<0.0001) and BAL neutrophil count (r=0.80, p<0.0001). We conclude that the concentration of H2O2 in breath condensate influences the ELF ascorbic acid concentration and provides a non-invasive diagnostic indicator of the severity of neutrophilic airway inflammation.

Effect of acute airway inflammation on the pulmonary antioxidant status.

Effects of acute airway inflammation induced by organic dust inhalation on pulmonary antioxidant status were investigated in healthy horses and horses affected by recurrent airway obstruction. Exposure to organic dust induced acute airway neutrophilia, which was associated with increases in elastase and decreases in ascorbic acid concentrations in bronchoalveolar lavage fluid. However, markers of oxidative stress were unaffected, as was hydrogen peroxide in breath condensate. Decreases in ascorbic acid correlated with increased respiratory resistance (P = .001) when both groups were combined. In conclusion, acute neutrophilic airway inflammation does not result in significant evidence of oxidative stress in horses affected by recurrent airway obstruction.

Antioxidant and inflammatory responses of healthy horses and horses affected by recurrent airway obstruction to inhaled ozone.

REASONS FOR PERFORMING STUDY Inhaled ozone can induce oxidative injury and airway inflammation. Horses affected by recurrent airway obstruction (RAO) have a decreased pulmonary antioxidant capacity, which may render them more susceptible to oxidative challenge. It is currently unknown whether RAO-affected horses are more susceptible to oxidative stress than those unaffected by RAO. OBJECTIVES To determine whether ozone exposure induces greater oxidative stress and airway inflammation in RAO-affected horses in remission than in healthy horses. METHODS Seven healthy control horses and 7 RAO-affected horses were exposed to 0.8 ppm ozone for 2 h at rest. RESULTS At baseline, bronchoalveolar lavage fluid (BALF) ascorbic acid concentrations were lower in RAO-affected horses than healthy controls. Ozone appeared to preferentially oxidise glutathione rather than ascorbic acid 6 h after exposure. Individual healthy and RAO-affected horses demonstrated oxidation of BALF glutathione after ozone exposure. Overall, RAO-affected horses did not demonstrate increased oxidative stress following ozone exposure, compared with healthy horses. Ozone did not induce significant airway inflammation in either group. CONCLUSIONS RAO-affected horses in remission are not more sensitive to ozone despite a decreased pulmonary antioxidant capacity. Sensitivity to ozone appears to be independent of initial pulmonary antioxidant status. POTENTIAL RELEVANCE Horses with high susceptibility to oxidative stress may benefit from antioxidant supplementation.

Pulmonary Bioavailability of Ascorbic Acid in an Ascorbate-synthesising Species, the Horse

Vitamin C (ascorbic acid) is a non-enzymatic antioxidant important in protecting the lung against oxidative damage and is decreased in lung lining fluid of horses with airway inflammation. To examine possible therapeutic regimens in a species with ascorbate-synthesising capacity, we studied the effects of oral supplementation of two forms of ascorbic acid, (each equivalent to 20 mg ascorbic acid per kg body weight) on the pulmonary and systemic antioxidant status of six healthy ponies in a 3 2 3 Latin square design. Two weeks supplementation with ascorbyl palmitate significantly increased mean plasma ascorbic acid concentrations compared to control (29 - 5 and 18 - 7 w mol/l, respectively; p <0.05 ). Calcium ascorbyl-2-monophosphate, a more stable form of ascorbic acid, also increased mean plasma ascorbic acid concentrations, but not significantly (23 - 1 w mol/l; p =0.07 ). The concentration of ascorbic acid in bronchoalveolar lavage fluid increased in five out of six ponies following supplementation with either ascorbyl palmitate or calcium ascorbyl-2-monophosphate compared with control (30 - 10, 25 - 4 and 18 - 8 w mol/l, respectively; p <0.01 ). Neither supplement altered the concentration of glutathione, uric acid or f -tocopherol in plasma or bronchoalveolar lavage fluid. In conclusion, the concentration of lung lining fluid ascorbic acid is increased following ascorbic acid supplementation (20 mg/kg body weight) in an ascorbate-synthesising species.

Comparison of the antioxidant status in tracheal and bronchoalveolar epithelial lining fluids in recurrent airway obstruction

REASONS FOR PERFORMING STUDY Following a period of airway inflammation the clearance of inflammatory cells along the mucociliary escalator may impose a considerable oxidant load on the trachea. OBJECTIVES To determine the degree of oxidative stress in tracheal epithelial lining fluid (ELF) in comparison to that present in peripheral airways after an acute exposure to organic dust. METHODS Tracheal wash fluid and bronchoalveolar lavage fluid (BALF) were collected for cytology and antioxidant analyses from 6 recurrent airway obstruction (RAO)-affected horses and 6 healthy control horses before and after stabling on straw bedding for 24 h. RESULTS In RAO-affected horses, organic dust exposure resulted in a significant decrease in ascorbic acid concentration in tracheal ELF (P<0.0001), which was greater than the decrease in bronchoalveolar ELF (P = 0.0003). The percentage decrease in tracheal ELF ascorbic acid correlated with the percentage decrease in bronchoalveolar ELF ascorbic acid (r = 0.76; P = 0.004) following exposure. CONCLUSIONS Acute organic dust exposure results in significant antioxidant depletion in the trachea, which may reflect inflammation and oxidative processes in peripheral airways. POTENTIAL RELEVANCE Further work is required to evaluate the role of ascorbic acid depletion in the pathogenesis of RAO.

The activity and expression of chitinase in the equine lung and its activity in normal horses and animals with recurrent airway obstruction.

Recurrent airway obstruction (RAO) is a chronic inflammatory condition in equine lung, which may share a common immunological basis with human asthma, in which dysregulated Th2 responses occur. Mammals express chitinases and chitinase-like proteins, two of which are active enzymes, chitotriosidase and acidic mammalian chitinase (AMCase). Both enzymes are upregulated in a range of inflammatory conditions, including asthma. We investigated the activity of chitinase in bronchoalveolar lavage fluid from horses with and without RAO in response to organic dust challenges. No significant differences were found in activity, although in one study RAO animals had elevated chitinase activity that fell short of statistical significance. The pH optimum and pH lability of the activity was consistent with the presence of chitotriosidase. RT-PCR amplification of the mRNA encoding chitotriosidase and AMCase in normal equine lung showed that chitotriosidase, but not AMCase, is expressed in trachea, bronchi, and peripheral lung tissue. The gene for chitotriosidase was identified from the Equus caballus (horse) genome 1.1 database and its similarity to the same genes from other species was determined. The results of this study indicate that the involvement of chitotriosidase in RAO is uncertain.